Band-i Mizan is a weir situated at the head of the Ab-i Girgir canal in Shushtar. The weir was originally constructed in the Sasanian period but has been renovated since, and a new esplanade has been constructed along the riverbank adjoining it. The weir may have originally been part of a larger project sponsored by the Sasanians to construct bridges, weirs, canals, and mills throughout the Khuzistan region.

The weir controls the flow of water into the Ab-i Girgir, a canal dug during the Sasanian period or possibly earlier that diverts waters from the Karun River through a gorge on the east side of Shushtar. The waters of the Ab-i Girgir were dammed further down the gorge to power a number of mills below. The weir has nine openings through which water from the Karun enters the canal.